C. elegans sensing of and entrainment along obstacles require different neurons at different body locations.

We probe C. elegans mechanosensation using a microfabricated platform where worms encounter a linear array of asymmetric funnel-like barriers. We found that sensing of and moving along barriers require different sets of neurons located at different parts of the animal. Wild-type worms sense and move along the barrier walls, leading to their accumulation in one side of the barriers due to the barriers' asymmetric shape. However, mec-4 and mec-10 mutants deficient in touch sensory neurons in the body exhibited reversal movements at the walls, leading to no accumulation in either side of the barriers. In contrast, osm-9 mutants deficient in touch sensory neurons in the nose, moved along the barrier walls. Thus, touch sensory neurons ALM and AVM in the body are required for C. elegans to sense and move along obstacles, whereas the ASH and FLP neurons in the nose are required only for sensing of but not moving along obstacles.